Ringer test circuit controlled from station under test



De@ 19, 1950 P. w. wADswoRTH RINGEB TEST CIRCUIT coNTRoLLED FROM STATION UNDER TEST s sheets-sheet 1 Filed 00t- 29, 1948 A 7' TOR/VEV De. -19, 1950 P. w. wADswoRTH `2,534,564 RINGER TEST CIRCUIT CONTROLLED FROM STATION UNDER' TEIST Filed Oct. 29, 1948 3 Sheets-Sheet 2 m R0.. www m0 VA WW.

H, M4 m A Dec. 19, 1950 P. w. wADswoRTH RINGER TEST CIRCUIT. CONTROLLED FROM STATION UNDER TEST Filed oct'. 29. 1948 3 Sheets-Sheet 3 m. om

/NVE/VTOR l? W WADSWORTH Patented Dec. 19, 95

RINGER TEST CIRCUIT co'NTRoLLED FROM STATION UNDER TEST Paul W. Wadsworth, Garden City, N. Y., assignor to Bell Telephone' Laboratories, Incorporated, New York, N. Y., a corporation of New York imputation october 29, 194s, serial No. 57,393

6 (llaims.`

rl`his invention relates to telephone systems in which connections between subscribers lines are established by automatic switching equipment and more particularly to a test trunk circuit for' enabling an outside repair man to test the ringer at a substation of a line from which substation he may initiate a test.

Trunk circuits of the type to which the present invention is directed are particularly applicable to a telephone system of the so-called cross bar type disclosed in the application of A. J. Busch Serial No. 521,394 led concurrently herewith.

When a repair man has completed adjustments or repairs or a subscribers substation apparatus, it is the usual practice to test the subscribers station apparatus either by requesting a call from a test desk operator at the central office or by dialing a connection to a test trunk circuit at the central oilce which is provided with the necessary equipment to automatically test the substation apparatus including the ringer.

In some exchange areas, subscribers lines of many different types may terminate in the same oice. These lines may be individual lines, twoparty lines, four-party semiselective lines, fourparty full selective lines7 eight-'party semiselective lines or ten-party ve code lines. It the repair man is to be enabled to test the substation apparatus on a line of any of these various types, it is essential that if he dials `a connection with a test trunk, that the test trunk be provided with means to apply the proper type of ringing to operate the ringer at the substation under test.

It is therefore an object of the present invention to provide improved automatic testing equipment at a central office which may be selected by dial operation at the substation under test.

It is a further object of the invention to pro; vide means responsive to the dialing of the numerical digits of the directory number of the substation from which a test call is originated, to cause the application of the proper type of ringing to operate the ringer of the calling substation.

These objects are attained in accordance with the present invention by the lprovision of ar small group of test trunk circuits, an idle one of which may be seized' and connected to a calling' line in response to the initiation of a test call from a sutation on the line by a repair man. To cause the selection of the test trunk circuit, the repair man dials the digits of a special oiiice code, indicative of the fact that he desires to make a test ofv the substation ringer, followed by the of the substation under test. The marker recognizes the special office code as a call for the test trunk circuit and the numerical digits give the marker the necessary information for identifying the type of ringing to be set up on a ringing selection switch associ-able with the test trunk circuit. When the trunk circuit is cut through to the subscribers station, a loud tone is placed on the line to inform the test man that the line has been cut through and to interfere with any other subscribers whose substations are on the same line conversing with each other. The trunk circuit is set for ringing by either dialing any arbitrary digit into the trunk circuit or by flashing the switchhook. When the repair man hangs up, the selected ringing current is connected to the line and continues until the repair man again lifts the receiver from the switchhook when ringing is tripped and the tone current is reapplied to the line. If the repair man desires to repeat the ringing test, he dials a digit again or ilashes the switchhook and following the restoration of the receiver to the switchhook the selective ringing current is reapplied to the line until the receiver is again removed from the switchhook. When the tests have been completed, the restoration of the receiver to the switchhook without dialing or flashing the switchhook will result in the restoration of the trunk circuit and the release of the connection to the trunk circuit.

The novel features of the invention are set forth in the appended claims and the invention as to its organization and its mode of operation will be best understood from the following detailed description when read in connection with the drawing in Which:

Fig. l shows schematically the equipment of an oiTice of the cross bar type by which a calling line may be connected to a station ringer test trunk? circuit;

Fig. 2 shows a station ringer test circuit; and

Fig. 3 shows a ringing selection switch circuit selectively operable to select the type of ringing required for operating the ringer at the substation of a line from which the test call' has been initiated by a test or repair man and for connecting the selected ringing current source' to the test trunk circuit.

The switches schematically disclosed in the boxes of Fig. l, labeled Line link'fraine andf Trunk linie frameV and the ringing selection switch of Fig. 3 fare of the lwell-known cross bar typasu'cli as is disclosed for example, in Patent No. 2,021,- 329granted- November 19, 1935 to J. N. Reynolds,

In the switch oi lilig. 3, the select magnets ar selectively operable from the marker in accordance with the setting of the number group to determine the type of ringing required for a speciiic connection and the hold magnets are individualized to ten trunk circuits, one of which may be a test circuit of the type disclosed in Fig. 2 to which the ringing selection switching circuit of Fig. 3 is common. A ringing selection switch circuit oi the type disclosed in Fig. 3 is more fully disclosed and described in the application ci lrl. C. Goddard Serial No. 57,385 illed concurrently herewith. The circuits and apparatus schematically disclosed in Fig. l of the drawing are fully disclosed and described in the application of A. J. Busch hereineeiore re ferred to.

rllhe invention will ncrv be considered in detail. It will be assumed that a repair man at the substation designated iet in llig. l, initiates a call whereupon a connection is established from the line link frame on which the calling line terminates, to an idle marker ld. Access to the marker is gained through the line link marker connector lili which connects only such leads as are necessary to identify the line link frame to the marker by its frame number and to inform the marker that a dialing connection is to be established. The marker ist then proceeds through its trunk and register selection control circuits |55 to select an idle originating register, such as is schematically disclosed by the box idR, which will later serve to transmit a dial tone to the calling line and to receive dial pulses.

Originating registers are distributed over the trunk link frames. By means of test leads extending from the registers to the marker, the marker determines which trunk link frames have idle registers and which frames are not being used by other markers. It then preierentially selects an idle with idle registers and conneots to the irame through the trunk link connector. rEhe marker then preferentially selects an idle register connects to it. It will be aS- sumed that the originating register l is idle and is accessible from the idle trunk link frame E55 which frame is connected to the marker through the trunk i i frame connector iii-t.

The location the calling line is begun as soon as the marker is seized and continues while the marker is selecting an idle register. Line 1ocation is made in ms of the line link frame, the vertical group, the iorizontal group and the vertical file. lollorker seizure, the marker determines whi h vertical group contains the line awaiting service. The vertical group contains a maximum of nity subscribers lines, therefore the determination of the vertical group localizes the subscribers lines within nity oi the maximum oi 65S lines terminating on the frame.

A line link horizontal group oi subscribers lines is one swi ch high and the width of the supplied line of switches, the maximum width being that ci a frame containing fourteen vertical groups. The marker determines which horizontal group has one or more lines within the selected vertical group awaiting service and the marker then preferentially selects one group. The line to be served has now been located within ve lines as determined by the selected vertical and horizontal groups.

Line location does not proceed past the horizontal group selection until the marker has seized the trunk link frame. Following trunk link frame seizure, the marker seizes the line link all frame 05 which has identified itself through its marker connector lill whereby leads are extended to the marker for vertical ille identification and for completing connection to the frame. A line link vertical le of subscribers lines is one vertical wide and ten switches high. Thus one vertical group contains five Vertical illes. The marker tests the ve lines found in the vertical file in which the calling line is located and ii more than one line are awaiting service, the marker preferentially selects one. The marker then transmits the line link frame number and the selected line location to the originating register.

After the horizontal group has been determined and an originating register seized, the marker selects one of ten channels which may be used to connect the calling line to the register. The marker tests the junctor, line link and trunk link in each channel to see what junctors or links are already in use on other calls. The lowest numbered available channel is chosen and the marker operates the select and hold magnets on the line link and trunk link frames to establish the channel. It has been assumed that the selected channel extends over the line link frame i'il and the trunk link frame When the channel is selected, the marker indicates to the register the number of the line link used in the channel and the register stores this information for future use.

After the channel has been established and checked, the marker releases leaving in the register the line link frame number, calling line location and the line link number used in the dialing connection to the register EDE.

The repair man then receives a dialing tone from the selected originating register after which the repair man proceeds to dial the digits oi? a special test code and the digits oi the assigned line number of the substation at which he is making repairs, which digit impulses are registered in the originating register. After the entire number has been dialed, the register calls in a marker over the originating register marker connector lill. As soon as a marker has been connected to the register, the register proceeds to transmit to the marker the calling line link frame location which is then registered in the calling line number register i5! of the marker, the digits of the special test code number which are registered in the called ofce codo register 52 of the marker and the numerical digits of the calling line number which are registered in the called line number register E53 of the marker. From the called ofiice code register |52, the marker proceeds through the translator circuit |54 to determine the routing oi' the desired connection thereby resulting in the operation of a route relay in the group of route relays 55. lt will be assumed that in the case under consideration the operated route relay is effective to control the setting up or" a connection from the subscribers line to the station ringer test trunk circuit shown in Fig. 2.

To accomplish this, the marker seizes an idle trunk link frame which has idle ringer test trunk circuits. It will be assumed that the trunk link frame i l5 is seized over the trunk link connector I l and connects to an idle ringer test trunk circuit, for example the trunk circuit shown in Fig. 2.

While trunk selection is taking place, the marker seizes the number` group frame ii?! over the number group connector H3 and passes the numerical digits of the calling line number to it from the called linenumber register |53. The number group gives the marker information for setting the ringing selection switch for ringing the substation on the cal-ling line. The trunk appears` on a vertical ille of the switch and different ringing codes appear on the horizo-ntals. The marker after receiving the required information from the number group, operates the selected= holdmagnet to connect the proper individual or party line ringing into the trunk. The marker then disconnects and leaves the switch held by the trunk circuit` After the marker has seized an idle station ringer test trunk circuit, it seizes the line link frame |06 on which the calling line terminates and selects an idle channel between the trunk circuit and the calling line. The dialing connection previously established is not released Iuntil the marker determines that an idle channel exists between the calling line and the trunk circuit.

The marker has recorded the number of the line link used in establishingl the dialing connection to the originating register |32 and may therefore reuse that line link as part o-i the originating connection if the link is part of the lowest numbered available channel. The marker then lproceed-stov operate the select and hold magnets on the line link and trunk link frames |06 and to establish a connection from the calling line lilo to the test trunk circuit of Fig. 2, over thev seleztedy channel. The marker now becomes disconnected and releases the originatingy register |102.

ItV has been assumed that the marker l@ has through the trunk line connector |09 been directed to the trunk link frame Il@ on which an idleV station ringer test trunk circuit terminates. There is a frame test (FI) lead 200 for each trunk link frame on which test trunk circuits' appear and each idle trunk circuit supplies ground from the lower back contact of the RC relayl 20|, over the upper normal contacts of the makebusy key EQ2 tor such test lead. The marker llasv access to the test leads, such as 200, through the trunk link connector lS- and knows that there is at least one idle trunk circuit on each frame corresponding to a grounded lead 200.

The marker then proceeds to select one of the frames withavailable trunk circuits and supplies ground on the frame (F) lead 2&3 to all the station ringer test trunk circuits appearing on that frame. cuit shown in Fig. 2 is one of such trunk circuits which appear on thetrunk link frame l0. This ground on leads 202iy is supplied over the lower normal contacts of the make busy MB key 252, over the inner lower back contact of the RC relay 20|', over the lower back contact of the Sl relay 204:- and to the right terminal of the winding of the F relay ESE of each trunk circuit that is idle. The marker determines which of the trunk circuits aren idlewhile looking for this ground through the windings of the F relays and. over the busy (B'll lead 206 selects one of the idle trunk circuits. These trunk link frames and trunk circuitV selections are carried out by the marker in the same general manner as the originating register selections previously referred to.

When a marker selects a trunk circuit, for example theorie disclosed in Fig. 2, it applies battery to the individua-l BT lead 206 thereby operating the F relayr 205 of such trunk circuit. Relay 295 upon operating locks over its inner upper contacts, over lead 253 to ground at the marker. When the markerselects-the trunk link fra-me |I 0 It will be assumed that the trunk cir-- 6. on which the trunk circuit oi Fig.k 2 appears, it locks out all other markers from such frame until the marker has completed setting up the connection.

Relay 235l upon operating connects ground. over its upper contacts to the FA lead Ztl extending to the trunk link connector tot for determining the cross-point in a horizontal level of a switch on the trunk link frame H0 where tl e appearance of the trunk circuit is located. The con.- nection of ground to the FA lead 251'! causes the operation of an FA relay (not shown) in the trunk link connector |09, which in turn causes theV operation of a level LV relay (not shown)- in the trunk link connector. The operation of the FA relay performs the necessary functions in conjunction with the marker to set up the connection. between the calling line llil and the.A trunk. circuit. One of these functions is the' transfer of the sleeve (S) lead 253 to the marker for testing and the tip conductor 2da and conductor 2| 0 of the trunk circuit to the marker for continuity checks. In addition, the operation oi? the LV relay of the trunk link connector establishes a cir'- cuit from the marker to the Si lead fill of the trunk circuit, thence over the inner lower contacts of the F relay 205 and through the wind-ing of the Sl relay 204 to battery and groundV so that the marker causes relay 23:1 to operate.

The marker at this time operates the select magnets on the trunk link frame M0 preparatory to cutting the connection through from the calling' line to the trunk circuit, the connection being held after cut-through by ground applied to the sleeve 208 of the trunk circuit through resistor 2|2 and over the inner lower contacts of operated relay 204. Relay 264 upon operating also applies tone current from the tone source 2|3 through resistor 2|`4, over the lower front contacts of relay 204, through condenser 2|`5 and over the lower No. 1 back contact of the RS relay 2|6 to ring conductor 2|!) of the trunk circuit. Over its upper contacts relay 204 supplies ground over the G lead 2|8 to the ringing selection. switch of Fig. 3 and connects operating ground over its inner upper contacts and conductor 2|9` tol contacts of several relays of the trunk circuit'.`

After the marker has operated the select magnets to out through the connection, it connects ground to the RC lead 220 and, with the F relay 205 operated, the circuit of the RC relay 20| is'y completed and relay 20| operates and locks over its upper contacts toA ground on conductor 2|9. At its lower back contact relay 26| removes ground from the FT lead 200 so that if all the trunk circuits on the trunk link frame become busy, the FT lead 200 will not be grounded and the trunk link frame will test busy to any marker. When relay 204r operated, it made the trunk circuit busy by opening the F leadv 2&3 at its lower back contact thereby opening the initial operating circuit of the F relay 295'. Relay 201| also upon operating opens the circuit of relay 205 at its inner lower back contact.

In the meantime, the marker has received information from the number group frame ||f2 concerning the type of ringing required to ring back over the calling line to operate the ringer at the substation where the repair man is testing. It will be recalled that the number groupframe has for this purpose received the numerical digits allocated to the substation from which the call has been made, which digits were dialed by the repair man. In accordance with this information supplied to themarker, the marker has operated select magnets of the ringing selection cross bar switch 302 of Fig. 3 allocated to the trunk circuits appearing on the trunk link frame H0. It will be assumed that for ringing the calling substation le@ the marker completes the circuit through the trunk link connector |69 and through the winding of select magnet 3E6 to ground to enable the application of negative superimposed ringing for two seconds followed by a four-second silent interval and also establishes a circuit for the number select magnet 3I0.

When the RC relay operates as previously described, it applies ground over its inner upper contacts and the H lead 22| to the winding of the hold magnet 36| whereupon such magnet operates and with select magnets 3l@ and 3l6 operated the cross-point contact sets 322i and 326 of the vertical row allocated to the trunk circuit of Fig. 2 become operated.

When the marker has completed its functions for this call, it releases the F relay 255 of the trunk circuit thereby opening the F, FA, RC and S1 leads 203, 261, 220 and 2i l. The removal of ground from lead 261 causes the cut-through of the connection between the calling line and the trunk circuit whereupon a circuit is established from battery through the lowei` winding of the L relay 222, over the lower No. l back Contact of relay ZIE, ring conductor 2li? or the trunk circuit, over the ring of the established connection, over the loop at the calling substation lim, returning over the tip of the established connection, tip conductor 269 of the trunk circuit, upper back contact of relay 2l6 and to ground through the upper winding or" relay 222. Relay 222 operates over this circuit and over its lower contacts establishes a circuit from ground on conductor 2I9 through the winding of the TL relay 223 to :battery whereupon relay 223 operates and establishes a circuit from ground on conductor 2N, over the inner contacts of relay 222 and the upper contacts of relay 223 through the winding of the Ll relay 224 to battery. Relay 224 thereupon operates and locks over its inner upper contacts, the upper back contact of the D relay 225, the upper back contact of the ST relay 225 and to ground on conductor 2i9.

The removal of ground from the Sl lead 2H opens the initial operating circuit for the Sl relay 264 but relay 224 being slow to release does not release prior to 'the operation of relays 222, 223 and 224 as just described and the reestablishment of a new holding circuit for relay 264 extending through its winding over the Alower contacts of relay 223 or of relay 222 to ground over the inner upper contacts of relay 264.

The connection being now cut through to the subscribers substation under test, the repair man may hear the loud tone applied to ring conductor 2l0 of the trunk circuit, transmitted over the established connection and returning over tip conductor 262 of the trunk circuit, the upper back contact of relay 2i@ and through condenser 211 to ground as a signal that a connection has been extended to a station ringer test trunk circuit. This loud tone on the calling' line is also effective to interfere with any other subscribers having substations on the same line conversing with each other while the tests are being conducted by the repair man. If the call is abandoned at this time and the repair man hangs up, the circuits will restore as later described.

To set the trunk circuit for ringing the repair man now dials a digit or ilashes the switchhook.

On the rst opening of the calling line loop, the L relay 222 releases followed by the release of the TL relay 223, but the L1 relay 224 being locked up, does not release and therefore a circuit is established from ground on conductor 2I9, over the back contact of relay 223, the upper contacts of relay 224, the lower back contact of relay 226 and through the winding of the RA relay 221 to battery and ground. Whereupon relay 221 opcrates and locks over a circuit extending over the lower back contact of relay 226, the upper contacts of relay 221, the upper normal contacts of the RB relay 228 and to ground on conductor 249 and thus relay RA remains operated long enough to insure the operation of the RB relay 228 on a short impulse. The operating circuit for relay 228 extends from ground on conductor 2|9, over the inner lower front contact of relay 221, the lower No. 5 back contact of RS relay 216, the lower back contact of the D relay 225 and through the winding of relay 228 to battery. Relay 228 upon operating locks over its upper alternate contacts to ground on conductor 2l9 so that it will remain operated following the release of relay 221 and, at its upper normal contacts, opens the locking circuit of relay 221 so that relay 221 will release upon the termination of the shortopening of the calling line loop.

Relay 221 upon operating also opens at its lower back contact the discharge path for condenser 229 extending through resistor 230, over which path the condenser has become fully discharged, and establishes a charging path for condenser 229 extending from ground over the lower front contact oi relay 221 through the condenser and resistor 23! to the +130-volt battery and the condenser 229 thereupon starts to charge. If the line loop is now reclosed within two seconds, which it should be in response to the release of the switchhook or the reclosure of dial contacts upon the return of the dial to normal, the L relay 222 Y will reoperate followed by the reoperation of the TL relay 223. Since the locking circuit for the RA relay 221 has now been opened by the operation of the RB relay 228, the release of relay 223 now causes the releaseof relay 221 which at its lower contacts opens the charging path for condenser 229 and closes the discharge path therefor to remove the partial charge from the condenser. The partial charge on condenser 229 has not been effective to cause the ring of the gas tube 232.

With relay 228 operated and relay 221 now released, a circuit is established from ground on conductor 2l9, over the inner lower back contact of relay 221, the inner lower contacts of relay 228 and through the winding of the ringing start (ST) relay 226 to battery and relay 226 operates and locks over its inner lower contacts, over the back contact or" the ringing trip (RT) relay 233, conductor 234 and the left contacts of the cross-point contact set 320, operated through the conjoint operation of the select magnet 3H] and the hold magnet 30l, tc ground applied to conductor 2li? by the operation of the S1 relay 204. At its lower back contact, relay 226 opens the operating circuit for the RA relay 226 to prevent the reoperation thereof and at its upper back contact opens the previously traced locking f circuit for the Ll relay 224. Relay 224 however remains operated under the control of the operated TL relay 223 and L relay 222. At its upper contacts, the ST relay 226 prepares the circuit for operating the RS relay 2I6.

When the call is from a one ring line, as will be assumed, the PU relay 235 is immediately operated without awaiting the closure of the interrupter contacts at the pick-up supply 236 connectable over the lower No. 3 contacts of relay 2I6 to conductor 231. Relay 235 in this instance is operated over a circuit extending from battery through the winding of relay 235, over the lower iront contact oi relay 226, the PKU lead 238, the left contacts of the cross-point contact set 326, closed through the conjoint operation of select magnet 3i6 and hold magnet 30 I, and the left contacts of the cross-point contact set 320, closed through the conjoint operation of select magnet 3I6 and hold magnet 30|, and thence to ground on conductor 2I8. Relay 235 upon operating locks over a circuit extending over the lower iront contact of relay 226, over its lower alternate 'contacts and to ground on conductor r2I8. Over its upper and inner lower contacts, relay 235 now connects the tip and ring leads 242 and 24E from the ringing selection switch circuit of Fig. 3 to the upper and lower No. l iront ccntacts of the RS relay 2 I6 preparatory to the application of ringing current to the calling line. Should additional dial impulses be received at this time, the L relay 222 and the TL relay 223 will follow the impulses but the Ll relay 221i being slow to release will remain operated.

When the repair man at the subscriber-1s substation hangs up after flashing the switchhook or dialing a digit as previously described, relays 222 and 223 release in turn permitting the release of the L'l relay 224. With relay 226 operated as previously described, the circuit of the RS relay 2 I 6 is now completed over the lower back Contact or" relay 224 to ground on conductor 2I9 and relay 2I6 operates to complete the ringing circuit. When relay 2l 6 operates it disconnects the windings of the L relay 222 from the tip `and ring conductors 200 .and .2!0 of the trunk circuit and also opens the circuit over which loud tone current was applied from the source 2I3. The Sl relay 201i is now held operated over the lower No. 2 contacts of relay 216. Relay 204 being kslow to release will remain operated over the interval intervening between the release of the L1 relay 224 and to the operation of relay 2 I 6. Relay 2 I 6 upon operating also opens at its lower No. 5 back contact the locking circuit of the RB relay 228 and such relay now releases.

Ringing current is now connected to the substation I00 from the ringing current supply 302, over the Code 1 generator lead, the right contacts of the cross-point contact set 3216, closed through the conjoint operation of select magnet .3I6 and hold magnet 30|, over the RT lead 239, through the Winding of the RT relay 233, the lower No. 4 contacts of the RS relay 2I6, the RB lead 240, the next-to-right contacts of cross-point contact set 320, operated through the conjoint operation of select magnet 3l!! and hold magnet 30|, the ring (R) lead 24I, over the inner lower contacts of the PU relay 235, the lower No. 1 front contact of relay 2I6, ring conductor 2I0 of the trunk circuit, thence over the ring of the established connection, through the ringer at substation Idil, over the tip of the established connection, tip conductor 209 of the trunk circuit, the upper front contact of relay 2I6, the upper Acontacts of relay 235, lthe tip (T) lead 242 and the next-toleft contacts of the operated cross-point contact set 320 to the ringing ground connection extending to the ringing :supply 302.

If the call is not for a one ring substation, the pick-.up relay 235 does not receive a d i- .l rect operating ground over the cross-point contacts of the ringing selection switch as just described but awaits an interrupter ground connection over the lower No. 3 contacts of relay 2I6, conductor '231, the lower normal contacts of relay 235, the lower front contacts of relay 226 and through the winding oi relay 235 to battery to insure that machine ringing will not start until the beginning of a ringing code. The selection and application of the proper ringing current to signal any subscriber on a party line of any type terminating in the cnice may be accomplished as fully set forth in the application of M. C. Goddard Serial No. 57,386 hereinbefore referred to.

When the receiver is removed at the substation under test, or at any other substation on the line, the ringing trip relay 23,?7 operates on the increased current flow thereby opening the locking circuit of the ST relay 226. Relay 226 now releases in kturn releasing the PU relay 235 'and the RS relay 2I6. With relays 2I6 and 23-5 now both released, the application of ringing current to the line i053 is discontinued and relay 233 now releases. The release of relay 2I6 reapplies the loud tone from source 2l 3 to the calling line and reconnects the windings of the L relay 222 to the calling line whereupon relay 222 operates followed by the operation of relays 223 and 224. Relay 224 upon operating recloses the holding circuit for the Sl relay 204 to maintain the latter relay operated following the release of relay 2I6 and locks as previously described under the joint control of the D relay 225 and the ST relay 226. The ycircuits are now restored to the condition in which ringing may be reapplied to the calling station if the repair man is desirous of repeating the test and redials or flashes the switchhook and then restores the receiver to the switchhook as previously described.

When the repair man hangs up without dialing a digit or flashing the switchhook, the L relay 222 and the TL relay 223 both release but the L1 relay 224 remains operated over its locking circuit. The RA relay 2.2i' is now reoperated in turn causing the reoperation and locking of the RB relay 228 in the manner previously described. At its lower contacts relay 221 opens the shunt around condenser 229 and closes the charging path through the condenser. Since the repair man has not dialed or iiashed the switchhook but has signaled a disconnect, relay 221 remains operated so that condenser 220 becomes fully charged and the potential on the lower cathode of tube 232, applied from the H3G-volt source through resistor 25E and through resistor 243, rises to a Value such that the tube becomes conducting and establishes a circuit from the +130- volt source, over the cathode-anode .path through the tube, over the lower contacts of the RB relay 228, through the upper winding and inner lower normal contacts of the D relay 225 and to ground over the lower contacts of the RA relay 221 and relay 225 operates. Relay 225 upon operating locks -through its lower winding and inner lower `alternate contacts to ground over the lower contacts of relay 22? and its lower back contact opens the locking circuit of the RB relay 228 which then releases and at its upper back contact opens the locking circuit of the Ll relay 224 which releases. Relay 225 at its inner lower alternate contacts opens the circuit traced through its upper winding and through the tube 232 thereby restoring the tube.

Relay 224 upon releasing, releases relay 221 which thereupon opens the charging path through the condenser 229 and closes the discharge path through the condenser to discharge the condenser. Relay 221 also opens the holding circuit of the D relay 225 which now releases.

Relay 224 upon releasing, opens the holding circuit for the S1 relay 204 which now releases and removes ground from sleeve conductor 208 of the trunk circuit thereby releasing the switches on the trunk link frame ll!) and the i line link frame I o6 to release the -connection between the calling line and the truck circuit of Fig. 2. Relay 204 also releases the RC relay which removes ground from conductor 22l thereby releasing hold magnet 3D! of the ringing selection switch of Fig. 3 to restore the vertical cross-point contact sets 320 and 325 of such switch. Relays 20| and 2M now being both released. the F lead 203 is closed through the Winding of the F relay 205 to the BT lead 20'6 and ground is reconnected to the FT lead 20G making the trunk circuit available for a new call.

The make busy key 252 is used to make the trunk Icircuit busy at any time. It may be onerated without interfering with any call that may be in the trunk circuit because it merely opens the FT and F leads 2M and 2fl3 which are already open if the trunk circuit is in use. When the trunk circuit is made busy and is not in use, the ground normally supplied to the FT lead 235 is applied to the MBL lead 244 to light a lamp common to the trunk circuits on the trunk link frame Ill! as an indication that there is a trunk on that frame which has been made busy. The kev 2F12 also transfers the circuit for operating the F relay 205 from the F lead 253 to the TF lead 245 whereby the marker can route a test call to a particular trunk circuit although it has been made busy. On such a call the marker will connect ground not only to lead 263 but also to lead 245.

What is claimed is:

l. In a telephone system. subscribers substation eouipments each including a ringer, a pulsing mechanism and a switchhook, a central oiice, lines connecting said substations with said central oilice, automatic switches at said central ofce, a ringer testing trunk circuit, a plurality of sources of ringing current, means under the control of the pulsing mechanism at a subscribers substation for controlling the operation of said switches to connect said substation with said trunk circuit and to select one of said sources of ringing current for connection with said calling substation, and means in said trunk circuit under the control of said switchhook to repeatedly connect and disconnect said one source of ringing current to and from said line while maintaining the established connection between said line and said trunk circuit.

2. In a telephone system, subscribers substation equipments each including a ringer, a pulsing mechanism and a switchhook, a central oliice, lines connecting said substations with said central office, automatic switches at said central office, a ringer testing trunk circuit, a plurality of sources of ringing current, means under the control of the pulsing mechanism at a subscribers substation for controlling the operation of said switches to connect said substation with said trunk circuit and to select one of said sources of ringing current for connection with said calling substation, means in said trunk circuit responsive to the momentary opening and reclosure of the line at said substation either by the operation of said switchhook or the operation of said pulsing mechanism with the switchhook in the receiVer-oi position to connect said one source of ringing current with said trunk circuit, means in said trunk circuit thereafter responsive to the opening of the line by the operation of the switchhook to the receiver-on position to apply ringing current from said trunk circuit to said line, and means in said trunk circuit thereafter responsive to the operation of said switchhook to the receiver-oii position for disconnecting said one source of ringing current from said line.

3. In a telephone system, subscribers substation equipments each including a ringer, a pulsing mechanism and a switchhook, a central oilice, lines connecting said substations with said central oiiice, automatic switches at said central office, a ringer testing trunk circuit, means responsive to the pulsing of the digits of a special oiilce code by the pulsing mechanism at a subscribers substation for controlling the operation of said switches to connect said substation with said trunk circuit, means responsive to the pulsing of the numerical digits of the assigned substation number for selecting that vone of said sources of ringing current required to operate the ringer of the calling substation for connection with said calling substation, and means in said trunk circuit under the control of said calling substation switchhook to repeatedly connect and disconnect said one source of ringing current to and from said line while maintaining the established connection between said line and said trunk circuit.

4. In a telephone system subscribers substation equipments each including a ringer. a pulsing mechanism and a switchhook, a central ofce, lines connecting said substations with said central office, automatic switches at said central olice, a ringer testing trunk circuit, a plurality of sources of ringing current, means under the control of the pulsing mechanism at a subscribers substation for controlling the operation of said switches to connect said substation with said trunk circuit and to select one of said sources of rineing current for connection with said calling substation, relay means in said trunk circuit responsive to the operation of said switchhook to repeatedly connect and disconnect said one source of ringing current to and from said line, a timing dcvice controlled by said relay means, and means responsive to said timing device for causing the release of the connection between Said line and said trunk circuit if said switchhook is maintained in a receiver-on position for a predetermined interval.

5. In a telephone system, subscribers substation equipments each including a ringer, a pulsing mechanism and a switchhook, a central oiiice, lines connecting said substations with said central oiiice, automatic switches at said central office, a ringer testing trunk circuit, a plurality of sources of ringing current, means under the controlof the pulsing mechanism at a subscribers substation for controlling the operation of said switches to connect said substation with said trunk circuit and to select one of said sources of ringing current for connection with said calling substation, a start relay for controlling the connection of said selected source of ringing current to said trunk circuit, a rst line relay operable in response to the connection of said trunk circuit to said substation, a secondary line relay operative in response to said first line relay and held operated under the control of said start relay, a first relay jointly controlled by said line relays and responsive to a momentary opening of the line at said substation by said pulsing mechanism or by said switchhook for causing the operation of said start relay, a second relay responsive to a reopening of said line for applying said ringing current to said line and a ringing trip relay responsive to the reclosure of said line to cause the release of said start relay whereby said source of ringing currentl is disconnected from said line, said relays recycling upon subsequent short openings and closures of said line to reapply and disconnect said selected ringing current to and from said line.

6. In a telephone system, subscribers substation equipments each including a ringer, a pulsing mechanism and a switchhook, a central office, lines connecting said substations with said central oice, automatic switches at said central office, a ringer testing trunk circuit, a plurality of sources of ringing current, means under the control of the pulsing mechanism at a subscribers substation for controlling the operation of said switches to connect said substation with said trunk circuit and to select one of said sources of ringing current for connection with said calling substation, a start relay for controlling the connection of said selected source of ringing current to said trunk circuit, a first line relay operable in response to the connection of said trunk circuit to said substation, a secondary line relay operative in response to said lirst line relay and held operated under the control of said start relay, a rst relay jointly controlled by said line relays and responsive to a momentary opening of the line at said substation by the operation of said pulsing mechanism or said switchhook for causing the operation of said start relay, a second -relay responsive to a reopening of said line for applying said ringing current to said line, a ringing trip relay responsive to the reclosure of said line to cause the release of said start relay whereby said source of ringing current is disconnected from said line, a timing device controlled by said iirst relay and a disconnect relay responsive to said timing device if said line is maintained open for more than a predetermined interval.

PAUL W. WADSWORTH.

REFERENCES CITED The following references are of record in the nie of this patent:

UNITED STATES PATENTS Number Name Date 1,586,587 Taplin June 1, 1926 1,647,256 Stokely Nov. 1, 1927 1,864,061 Gooderham June 21, 1932 2,188,520 Wochinger Jan. 30, 1940 

